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IF humans made Australia a continent swept by fire, and dominated by fire-friendly eucalypts, maybe humans can also re-shape our landscapes into more diverse, less fire-prone places: so muses University of Tasmania ecologist Chris Johnson.

Professor Johnson led a forensic research program which last week reported the best evidence yet that human hunters killed off Australia's megafauna, the giant animals that walked the continent until about 40,000 years ago.

The research showed that in taking out the megafauna, humans removed grazing pressure from the landscape and unwittingly promoted fire to its central place in Australian ecosystems.

Australia's megafauna included at least 20 families of marsupials, monotremes, birds and reptiles, including 2.5-tonne wombats, two-metre kangaroos, great horned turtles and a marsupial version of the lion.

They died out around 40,000 years ago, several thousand years after Aboriginal people occupied the continent.

Prof Johnson's team dug into an ancient swamp in Lynch's Crater in Far North Queensland and came up with a 130,000-year record that included a vital indicator: Sporormiella, a fungus that needs to be eaten by a herbivore to complete its life cycle so it can reproduce in the animal's dung.

Across the world, Prof Johnson said, large numbers of Sporormiella are associated with large amounts of dung, and therefore large herbivores.

In the Lynch's Crater cores, the fungus was consistently on the record in abundance until around 40,000 years ago, pointing to the presence of large herbivorous animals up to that point. Then it all but vanished.

At the same point, the content of the cores changed in other ways.

Previously, the pollen in the cores suggested a mixed landscape. In Prof Johnson's reading of the record, this probably meant patches of grassland and sedges dotted with mixed rainforest and woodland, in a climate believed to be cooler and drier than today.

About 100 years into the decline of Sporormiella in the cores, abundant charcoal appeared on the record. This indicator of fire seldom appeared on the core record before 40,000 years ago, but then remained a strong presence up to the present day.

About 300 years after Sporormiella's decline, grass pollen became increasingly abundant. Eucalypt pollen surged after 400 years.

Prof Johnson said the pollen began to record more uniform vegetation. Without large browsers and grazers to form patches of grassland in the forest, dry forest pollen has dominated the record for much of the past 40,000 years.

Because the charcoal appeared on the record after Sporormiella declined, this seemed to rule out the theory that fire was responsible for megafauna extinction, Prof Johnson said.

Climate change was also ruled out, because there were no significant climate shifts at the time the animals became extinct, and they had survived climate shifts in the past.

That left humans in the dock - as they are for megafauna extinctions in Madagascar, New Zealand, Europe and the Americas, although scientific debate still rages over the extent of their guilt.

Prof Johnson has done some analysis on whether a small number of humans can wipe out a continent's worth of large animals within a few thousand years, and he has no doubt they could.

"The big animals have very slow reproduction. You don't need to kill very many in a given time to exceed their ability to replace themselves. That means extinction. It's a very predictable, plausible scenario."

Still, Prof Johnson wants to do similar studies in other parts of Australia to see whether the pattern repeats.

And while some scientists applauded the study as the most conclusive yet to implicate humans in megafauna extinction, others said it was flawed and climate change was still the most likely cause.

•"The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia" was published in Science, March 23.

I agree with the article Ben, but I don't get too tied up in the scientists view of attaching guilt to the scenario. People have always tried to make decisions with their own self interest at the forefront as that is simply survival instinct & we still react in that way. Understanding the ramifications of what we do can be quite difficult, particularly for the long term. In a way I believe this scenario is really positive, because if we can impact our environment that way, then surely we have the ability to reverse that impact by doing the opposite. Seems too simplistic for some but from personal experience I think it is possible.

Welcome on board Graham.
Yeah good points you make in my opinion too.
I think a major hurdle to get over is perceptions of what "pristine" is and the assumption that the Aboriginals did burning for some other reason than feeding themsleves and having somewhere safe to camp.
I do think that until the community understands the past it is very difficult to establish a viable future pathway.